Opti-mechanical devices for displaying small displacements or movements based on a change in color to indicate tension are described in U.S. Pat. No. 3,987,699 (Popenoe), U.S. Pat. No. 4,904,132 (Popenoe), and U.S. Pat. No. 5,189,979 (Popenoe). Regardless of the benefits provided by these devices such devices have hitherto been difficult and time consuming to manufacture. Thus, there is a need for faster ways of manufacturing fasteners fitted with tension displacement indicators.